Tunnel refurbishment/upgrading should be conducted in such a way that the negative impact on the environment is as low as reasonably practicable. This can be obtained by:
Tunnel refurbishment/upgrading can in many cases provide an opportunity to improve the environmental impact of the infrastructure as a whole, either through changes to the tunnel’s design or to its equipment.
In terms of design, an example of a major refurbishment project conducted with environmental issues in mind is the Croix Rouse tunnel in Lyon (France). In order to upgrade the tunnel’s safety standards, the initial tube has been linked to a new parallel escape gallery via cross-passages every 150 metres, thereby enabling the evacuation of users. The tunnel owner wished to give additional functions to this escape gallery by allowing its use by public transport (buses) and environmentally-friendly modes such as pedestrians and cyclists. This is an interesting example of the sustainable use of infrastructure for purposes other than those for which it was initially intended.
In terms of tunnel equipment, refurbishment/upgrading can provide an opportunity to reduce energy consumption. The main energy-consuming families of equipment in a tunnel during normal operation are lighting, ventilation, safety devices (signalling, closed circuit television CCTV, etc.) and pumping facilities (in subsea tunnels or when there is water seepage). The respective share of each of these energy-consuming systems varies greatly, depending on the specific characteristics of the tunnel: length, gradient, water ingress, etc. In terms of optimization during refurbishment/upgrading, lighting and ventilation systems are those which provide the highest potential energy savings.
Actions taken on lighting during refurbishment/upgrading are primarily designed to better define the lighting requirements in the entrance zone, which is the most heavily lit. Solutions implemented may:
Other actions may concern the optimization of interior zone lighting. At the moment, most experiments, and in some cases test sites, involve the use of LEDs (light emitting diode) sources.
An example of energy-saving measures implemented to ventilation during refurbishment/upgrading is the installation of jet fans with inclined outlets. It has been shown that these jet fans can enable a significant improvement in the in-tunnel thrust obtained and a reduction in energy consumption.
Outside air quality (at tunnel portals or vitiated air extraction systems) can be improved during refurbishment/upgrading, through increased stack heights or by the installation of vitiated air treatment systems (air cleaning systems). In some countries, vitiated air treatment systems have been put in place (Spain, Japan, Italy, Norway France….). However, after some years of use, the conclusions regarding the efficiency of air cleaning are different from one country to another. The decision to use such systems therefore has to be carefully analysed, taking into account several criteria (investment costs, efficiency, maintenance, etc.).
Finally, tunnel refurbishment or upgrading can provide an opportunity to assist in the preservation of the animal species living around the tunnel. Measures that can be implemented include restoring passageways for certain species or preserving reproduction areas.
General environmental questions related to the design, construction, operation and refurbishment of tunnels are dealt with in the technical report 2017R02EN “Road tunnel operations: First steps towards a sustainable approach”.
Questions relating to the tunnel impact on outside air quality are dealt with in report Technical Report 2008 R04 "Road Tunnels: A Guide to Optimizing the Air Quality Impact upon the Environment".